In any type of can, steel sheets for use in cans (steel sheets for containers) have conventionally been coated but in recent years a film lamination technique has drawn attention as a technique to replace coating and has spread rapidly from the viewpoint of global environmental protection.
A chromate coating has conventionally been formed on a steel sheet for use in the undercoat of a laminated film but recently there have started to be calls for restrictions to be imposed on the use of hazardous substances such as lead and cadmium and for attention to be paid to the working environment of manufacturing plants and there have been requests to stop the use of a chromate coating.
In the beverage container market, cans face competition from containers such as PET bottles, bottles and drink boxes in terms of cost and quality, and steel sheets for laminated containers are also required to have more excellent formability in can manufacture (in particular, in terms of film adhesion, formed film adhesion, corrosion resistance).
For example, Patent Literature 1 discloses, as a steel sheet meeting such requirements, a steel sheet for containers having a zirconium compound coating formed on the steel sheet by subjecting the steel sheet to immersion or electrolytic treatment in a solution containing zirconium ions, fluorine ions, ammonium ions and nitrate ions, the coating weight of the zirconium compound coating being 1 to 100 mg/m2 in terms of zirconium metal content and up to 0.1 mg/m2 in terms of fluorine content ([Claim 1]).